Since the earliest description of the adult respiratory distress syndrome (ARDS), impaired lung compliance has been a key diagnostic feature. Newer data suggest that a clear understanding of the mechanisms of acute lung injury may be needed to select the ventilatory pressures and patterns of flow delivery required for optimal gas exchange, adequate oxygen supply to tissue, and avoidance of barotrauma. This discussion briefly reviews the ARDS-specific derangements of lung mechanisms, describes measurement techniques applicable to the clinical setting, and suggests ways in which such information can be used in patient management.